The embodiment relates to a light emitting device, a light emitting device package, and a lighting system.
A light emitting device (LED) includes a p-n junction diode having a characteristic of converting electric energy into light energy. The p-n junction diode can be formed by combining group III and V elements of the periodic table. The LED can represent various colors by adjusting the compositional ratio of compound semiconductors.
When forward voltage is applied to the LED, electrons of an n layer are bonded with holes of a p layer, so that energy corresponding to an energy gap between a conduction band and a valance band may be generated. This energy is mainly realized as heat or light, and the LED emits the energy as the light.
A nitride semiconductor represents superior thermal stability and wide band gap energy, so the nitride semiconductor has been spotlighted in the field of optical devices and high-power electronic devices. In particular, blue, green, and UV light emitting devices employing the nitride semiconductor have already been developed and extensively used.
Meanwhile, a light emitting device including the nitride semiconductor can be classified into a lateral type light emitting device and a vertical type light emitting device according to positions of electrode layers.
However, the vertical type light emitting device has a difficulty in the manufacturing process because a non-conductive substrate has to be separated after the nitride semiconductor has been formed over the non-conductive substrate such as a sapphire substrate. Accordingly, researches and studies have been actively carried out toward a nitride semiconductor light emitting device that does not require the separation of a substrate by using a conductive substrate when the vertical type light emitting device is manufactured.
For example, according to the related art, a nitride semiconductor layer may be formed over a gallium oxide substrate.
However, according to the related art, the nitride semiconductor layer may be delaminated from the gallium oxide substrate.
For example, the gallium oxide is easily etched at a high temperature hydrogen gas atmosphere, but the nitride semiconductor layer is grown at a high-temperature atmosphere of the mixture of ammonia gas and hydrogen gas. Therefore, when the nitride semiconductor layer is grown, a portion of the interface between the gallium oxide substrate and the nitride semiconductor layer is irregularly etched by hydrogen gas at a high temperature. The irregular etching of the interface degrades the adhesive strength of the interface, thereby causing the delamination between the nitride semiconductor layer and the gallium oxide substrate.
In addition, the gallium oxide substrate has a thermal expansion coefficient different from that of the nitride semiconductor layer. Accordingly, when the nitride semiconductor layer is cooled after the nitride semiconductor layer has been grown, or when a heat treatment process is performed in order to manufacture the light emitting device, the delamination may be caused at the interface between the gallium oxide substrate and the nitride semiconductor layer due to the stress caused by the difference in the thermal expansion coefficient between the gallium oxide substrate and the nitride semiconductor layer.